A metal-oxide-semiconductor (MOS) transistor is one of the most important devices in contemporary integrated circuits. Basic structure of the MOS transistor includes: a semiconductor substrate; a gate structure on a surface of the semiconductor substrate; a doped source region in the semiconductor substrate on one side of the gate structure and a doped drain region in the semiconductor substrate on the other side of the gate structure. In the MOS transistor, a voltage is applied on the gate structure to a control current flowing through a channel at a bottom of the gate structure and to produce on/off switch signals.
With continuous development of semiconductor technologies, conventional planar MOS transistors have poor ability to control the channel current and a severe leakage current problem. A fin field effect transistor (FinFET) is a newly developed multi-gate device. A FinFET includes a fin protruding from the surface of the semiconductor substrate, a gate structure covering a portion of the top surface and sidewall of the fin, a source doped region in the fin on one side of the gate structure and a drain doped region in the fin on the other side of the gate structure.
However, semiconductor devices made of either planar MOS transistor or FinFET have poor performance.